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Chemistry homework Assignment

Chemistry homework Assignment

scale factors were obtained before and after each experi- ment from separate audio side band spectra which were derived from Hi and located within several hertz of the original satellites. In each case, the before and after scale factors agreed to less than 0.001 Hz/cm.

For all seven temperature experiments described above, the average scale factor never varied by more than 0.02 Hz/cm, and most values were within 0.01 Hz/cm of the average, 0.99 Hz/cm. In the remaining temperature experiments, an audio side band, generated by a frequency of 8.6-9.2 Hz, was produced from one transition of the satellite doublet, and measured with respect to the remaining transition about 1.5 Hz away. At any temperature, a maximum expected error of 0.02 Hz/cm in the above average scale factor (0.99 Hz/cm) would introduce a maximum total scaling error of 0.03 Hz in Jcc but for most cases, the scaling error is thought to be less than 0.01 Hz. Nmr data for 3 are shown in Table III.

Experimental Section 2.3- Dideuterio-l,3-butadiene (2). 2,3-Dideuterio-2,3-butanediol

was prepared by reduction of biacetyl with lithium aluminum deuteride according to the procedure of Loewus, Westheimer, and Vennesland.32 The crude 2,3-dideuterio-2,3-butanediol was dis- tilled through a Vigreux column under vacuum, and the major frac- tion was collected at 89-92° (21 mm) (reported 95-105° (40 mm)).

2.3- Dideuterio-2,3-butanediol was acetylated in the usual man- ner33 using an excess of acetic anhydride and pyridine. The crude product was distilled through a Vigreux column, and the major

(32) F. A. Loewus, F. H. Westheimer, and B. Vennesland, J. Amer. Chem. Soc., 75, 5018 (1953).

(33) L. F. Fieser and M. Fieser, “Reagents for Organic Synthesis,” Wiley, New York, N. Y., 1967, p 958.

6375

fraction of 2,3-dideuterio-2,3-diacetoxybutane was collected at 94.0-94.5° (22 mm).

2,3-Dideuterio-2,3-diacetoxybutane (3 g) was added dropwise into a heated Vycor column containing Vycor chips under an atmosphere of N2 at 585°, using the procedure of Shlechter, Othmer, and Brand.34 The crude gaseous product was purified by passage through an ice-cooled trap, followed by a bubbler containing 10% aqueous sodium hydroxide solution and a second bubbler con- taining water. The wet gas was passed through a tube containing a weighed mixture of carbon disulfide and hexamethyldisilane. The nmr tube, which was immersed in a Dry Ice-acetone bath, was evacuated and sealed under vacuum. The mixture was found to be 8.3% (w/w) 2,3-dideuterio-1,3-butadiene (2) and 4.6% hexa- methyldisilane in carbon disulfide solvent.

1,1,4,4-Tetradeuterio-l,3-butadiene (3). 2,2,5,5-Tetradeuterio- 2,5-dihydrothiophene 1,1-dioxide was prepared from sulfolene by alkaline deuterium exchange according to the method of Cope, Berchtold, and Ross.35 Eight exchanges yielded 99.3% isotopic purity (by nmr integration). Recrystallization from 2:1 THF- pentane gave a mp 63-65° (reported mp 66.8-67.3°).

The above dihydrothiophene 1,1-dioxide (5 g) was pyrolyzed at 130° to generate 3 at a convenient rate. Gaseous 3 was bubbled through two traps, each containing about 100 ml of 10% aqueous sodium hydroxide solution to remove the sulfur dioxide by-product formed in the reaction. The purified 3 was passed through a tube containing Drierite, and into two preconstricted tared nmr tubes containing known weights of hexamethyldisilane. The nmr tubes were immersed in Dry Ice-acetone contained in a dewar flask. In order to minimize boiling of 3 during high temperature experi- ments, one of these filled nmr tubes was sealed under nitrogen at atmospheric pressure. The second nmr tube, sealed under vacuum, was used for the remaining variable-temperature study. Both samples contained 11 % (w/w) hexamethyldisilane in neat 3.

Acknowledgment. The authors are grateful to the National Science Foundation for Grant No. GP- 3815 which provided support for this work.

(34) N. Shlechter, D. F. Othmer, and R. Brand, Ind. Eng. Chem., 37, 905 (1945).

(35) A. C. Cope, G. A. Berchtold, and D. L. Ross, J. Amer. Chem. Soc., 83, 3859 (1961).

Conformational Analysis of 2-Methylbutane1 Robert L. Lipnick and Edgar W. Garbisch, Jr.*2 Contribution from the Department of Chemistry, University of Minnesota. Minneapolis, Minnesota 55455. Received November 9, 1972

Abstract: The AB2 deuterium-decoupled pmr spectrum of 2-methylbutane-d9 (1) was determined at ten tempera- tures in the range —91 to +72°. The observed temperature dependences of the three nmr parameters (va, vs, and Jab) were ascribed to changes in conformer population with temperature (eq 1). These parameters were subse- quently used in a least-squares analysis to obtain quantitative estimates of AH and the intensive nmr parameters of conformers la and lb. The value of AH for the equilibrium la ^ lb is 888 ± 18 cal/mol ( 5 = —1.376 eu). The torsional angle, a, for la was estimated to fall between 60 and 72° from the calculated vicinal coupling con- stant.

Rotational isomerism in 2-methylbutane has been

. observed by Raman,3 infrared,4 ultrasonic,5 and thermodynamic6 methods, and estimates were made of

(1) Presented in part by R. L. L. at the 23rd Congress of Pure and Applied Chemistry, Boston, Mass., July 1971.

(2) Correspondence may be directed to E. W. G., Center for Applied Research in Environmental Sciences, St. Michaels, Md. 21663.

(3) G. J. Szasz and N. Sheppard, J. Chem. Phys., 17, 93 (1949). (4) J. K. Brown and N. Sheppard, J. Chem. Phys., 19, 976 (1951). (5) J. M. Young and A. A. Petrauskas, J. Chem. Phys., 25, 943

(1956). (6) D. W. Scott, J. P. McCullough, K. D. Williamson, and G. Wad-

dington, J. Amer. Chem. Soc., 73, 1707 (1951).

both the enthalpy difference between the two possible conformers and their barrier to interconversion.

Szasz and Sheppard concluded from Raman3 that the enthalpy difference for the equilibrium la lb was

Lipnick, Garbisch / Conformational Analysis of 2-Methylbutane

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6376

Figure 1. The 60-Mc/sec nmr spectra of 1 at (a) 35.5° with deu- terium decoupling, (b) 35.5° without deuterium decoupling, and (c) the calculated theoretical spectrum using the spectral parameters obtained from laocoon3 at 35.5°.

either less than 200 cal/mol or greater than 1000 cal/mol. Brown and Sheppard4 drew no quantitative conclu- sions from their infrared study. Scott and coworkers6 concluded from their heat capacity measurements that the C, conformer, lb, is at least several thousand cal/ mol less stable than la, the C, conformer. More re- cently, Au-Chin,7 using theoretical considerations, has estimated AH for la lb as 1.33 kcal/mol.

This work attempts to confirm through variable- temperature nmr that la is the more stable conformer in the equilibrium la lb and to determine more pre- cisely the enthalpy difference between la and lb. In addition, the derived vicinal coupling constants will be used to estimate the torsional angle, a, for the Cj con- former.

Results and Ace my homework – Write my paper – Online assignment help tutors – Discussion Under conditions of deuterium decoupling, 2-methyl-

butane-t/g (1) gives rise to eight nmr transitions, corre- sponding to a spectrum of the type AB2.8 Initial values of va, vb, and Jab were obtained from eq 1-3,9 where

were subsequently inputed into iterative laocoon310 calculations along with the corresponding experimental frequencies of all eight transitions to obtain best least- squares values of vK, vB, and JAb. Figure 1 shows un- decoupled and deuterium-decoupled spectra of 1 along with a laocoon3 computed spectrum.

These laocoon3 derived parameters were used in- dependently to determine the best solution values to eq 411,1 s where Paj and PbJ are the y’th of / intensive param- eters of conformers la and lb, and Ptf is the y’th of / observed parameters at the /th of k temperatures, <;. As solution of eq 4 varying all of the unknowns, in-

P,j – , =

—AH AS Ptf – ¿V RTij + R (4)

eluding AH and AS, was not achieved, it was found necessary to reduce the number of unknowns by one through assuming AS = —R In 2 (—1.376 eu), the statistical value corresponding to two enantiomeric Cs conformers.14

A number of requirements which must be satisfied for the quantitative application of eq 4 to conformational analysis have been discussed critically.13 It is essential that P&j and Pb¡ both be temperature independent so that the observed temperature dependences, °, reflect only changes in conformer population. We use as an operational criterion of this condition, the self-consis- tency of the independent eq 4 solution values of AH provided by the respective nmr parameters and the chemical shift difference, . These solution values of AH obtained in the single parameter calculations are presented in Table I (solutions 1-4). They are seen to fall within the probable errors of one another, and therefore meet our operational criterion for the temper- ature independence of the respective intensive param- eters. Therefore, it is felt justified to use as the most reliable solution of eq 4 these values obtained in a single combined parameter calculation of vA, vB, and Jab (solution 4). This multiple parameter calculation leads to an enthalpy difference AH – 888 ± 18 cal/mol at AS = —1.376 eu for the equilibrium la ^ lb. Figure 2 shows the theoretical temperature dependences of va, vb, and Jab corresponding to solution 5 (Table I) along with the experimental values of these parameters.

The derived vicinal coupling constants for conformers la and lb obtained in solution 5 of Table I allow us to estimate the torsional angle, a, for the Ct conformer la, using the theoretical relationship15 between dihedral angle, , and vicinal coupling, J

J = A(cos2 + n cos ) (5) In these calculations, the projected torsional angle, , in both la and lb is assumed to be 120°. Since the C,«

VA = Vl (1)

VB = (v¡ + Vl)¡2 (2) Jab = Vs[(vs — ve) + (v4 — n)] (3)

va and vB are the chemical shifts of HA and HB (relative to hexamethyldisilane), and Jab is the vicinal proton coupling across the 2,3 C-C bond. These initial values

(7) T. Au-Chin, Sci. Sínica, 3, 279 (1954). (8) See J. Lee and L. H. Sutcliffe, Trans. Faraday Soc., 55, 880

(1959). (9) E. W. Garbisch, Jr„ J. Chem. Educ., 45, 402 (1968).

(10) S. M. Castellano and A. A. Bothner-By in “Computer Programs for Chemistry,” Vol I, D. F. Detar, Ed., W. A. Benjamin, New York, N.Y., 1968, pp 10-39.

(11) See ref 12 and references cited therein. (12) R. L. Lipnick and E. W. Garbisch, Jr., J. Amer. Chem. Soc.,

95, 6370 (1973). (13) E. W. Garbisch, Jr., B. L. Hawkins, and K. D. MacKay in “Con-

formational Analysis: Scope and Present Limitations,” E. Chiurdogu, Ed., Academic Press, New York, N. Y., 1971, pp 93-110.

(14) The entropy of mixing is normally used to account for any entropy differences between conformers. See E. L. Eliel, N. L. Allinger, S. J. Angyal, and G. A. Morrison, “Conformational Analysis,” Wiley. New York, N. Y., 1965, pp 11-12.

(15) M. Barfield and D. M. Grant, Advan. Magn. Resonance, 1, 149 (1965).

Journal of the American Chemical Society j 95:19 / September 19, 1973

Table

I.

Solution

Parameters”

of

Equation

1

Using

Temperature

Dependences

of

Jab,

pa,

pb,

and

¿ab

at

Fixed

Values

of

5

6377

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Figure 2. The experimental temperature dependences of pa (0), pb (·), and Jab (A), along with their theoretical dependences (solid lines). The theoretical dependences (solid lines) were derived from the combined parameter solution of eq 5 (solution 5 of Table I).

conformer (lb) is symmetric, the derived coupling 16 is given by eq 6. For the C¿ conformer (la), the

Jb = 3.52 Hz = A(cos2 60° + n cos 60°) (6) corresponding coupling is given by eq 7,17 where a is

= 7.06 Hz = -“-4–· =

A(COS2 a + « COS a) + A(cos2 ( + a) + « COS ( + a)) 2

(7)

the torsional angle between the two gauche related methyl groups. Application of eq 5 to the experi- mental vicinal couplings for the series ethane, propane, and isobutane allows an estimate to be made of the value for A for a series of hydrocarbons obtained by increasing methyl substitution of an ethane skeleton. For ethane, propane, and isobutane, the experimental vicinal coupling, JviCinai, is given by eq 8, where 0g =

_

2/e + _

«’vicinal ^

2^(cos2 + n cos 0g) + /4(cos2 4 + n cos 4) 1 (8)

60° and = 180°. Simplification of eq 8 leads to eq (16) Ja and Jb refer here to the vicinal interproton couplings across

the 2,3 C-C bond for conformers la and lb, respectively. (17) Je and Jt refer to the gauche and trans vicinal interproton cou-

plings across the 2,3 C-C bond for conformer la.

Lipnick, Garbisch / Conformational Analysis of 2-Methylbutane

6378

N

Figure 3. The dependence of A (eq 10) as a function of the number of methyl groups substituted on ethane for ethane (a), propane (b), isobutane (c), cyclohexane (d), and butane (e). The triangles (f) indicate values of A for 2-methylbutane corresponding to a = 60, 66, and 72°.

9. In Figure 3, A is plotted as a function of the number A 3Jvicinal/1 *50 ^Aioinal (9)

of methyl substitutions, N, for the series ethane,18 propane,19 isobutane,20 butane,21 and cyclohexane.22 The qualitative decrease in A with increasing substitu- tion probably limits A to a value no greater than 13.6 Hz, the largest such coefficient obtained for a disub- stituted ethane. This value of A is found to corre- spond to = 0.02 and = 72° upon simultaneous solu- tion of eq 6 and 7. The lower limiting value for is 60° ( = 0.10, A = 11.7 Hz), corresponding to no in- crease in the normal sp3-sp3 torsional angle. The gauche conformer of «-butane (A = 12.56, = 0.11), a similar system with one gauche methyl-methyl inter- action, has been found to be skewed 66°.21·23 The gauche butane value for the torsional angle, which is probably the best empirical estimate for a, falls be- tween the lower and upper limits (60-72°) obtained above.

It is of interest to compare the enthalpy change la lb (AH = +888 ± 18 cal/mol) with that found for the comparable butane equilibrium 2a +; 2b (AH =

ch3 h 2a 2b

+681 ± 35 cal/mol).21 In both equilibria, conformer a is the energetically more favorable form due to an additional methyl-methyl interaction present in b. For gauche butane (2b), this steric interaction is par- tially relieved by an increase in the torsional angle. The Cs conformer of 2-methylbutane, lb, contains two symmetrical methyl-methyl interactions, and cannot undergo torsional deformation. If the additional enthalpy change for la lb over 2a ;=± 2b of 207 cal/ mol is due to unrelieved methyl-methyl interactions,

(18) R. M. Lynden-Bell and N. Sheppard, Proc. Roy. Soc., Ser. A, 269, 385 (1962).

(19) D. R. Whitman, L. Onsager, M. Saunders, and . E. Dubb, J. Chem. Phys., 32, 67 (1960).

(20) J. S. Waugh and F. W. Dobbs, J. Chem. Phys., 31, 1235 (1959). (21) P. B. Woller and E. W. Garbisch, Jr., J. Amer. Chem. Soc., 94,

5310 (1972). (22) E. W. Garbisch, Jr., and M. G. Griffith, J. Amer. Chem. Soc.,

90, (6543 1968). (23) K. Kuchitsu, Bull. Chem. Soc. Jap., 32, 748 (1959).

then each such interaction is equivalent to an increase in enthalpy of approximately 104 cal/mol. This anal- ysis would predict an enthalpy difference of approxi- mately 785 cal/mol (681 + 104) for the equilibrium 3a =5 3b of 2,3-dimethylbutane. This estimate is in

qualitative agreement with the value of 0.95 kcal/mol,24 obtained by ultrasonic absorption, in which the ex- pected tolerance is approximately ± 400 cal/mol.25

Nmr Spectral Determinations. High resolution deu- terium-decoupled nmr spectra were taken on a modified Varían A-60 nmr spectrometer, as described pre- viously.12 Spectra were obtained from a neat sample of 2-methylbutane-<f9 containing ~10% (v/v) hexa- methyldisilane, and sealed under vacuum. Spectra were determined at ten temperatures from —91 to +72°, and 12-22 spectra were recorded at each temper- ature. Frequencies for each transition were calculated from the center at half-height of each peak from audio side band calibration. Scale factor corrections ranged from 0.984 to 0.991 Hz/cm. Average values and the corresponding standard deviations were calculated for each transition and any frequency values whose devia- tions were greater than twice the standard deviation for that transition were automatically discarded. This process was repeated automatically until experimental values were no longer discarded.

Initial values for ¡ , vb, and As which were obtained from eq 1-3 were used as input for least-squares lao- coon3 calculations. For each temperature, any transi- tion whose average experimental frequency differed from the corresponding calculated value by more than twice the laocoon3 calculated standard deviation was discarded, and allowed to vary in a second iterative calculation. Table II shows the final results for ten temperatures.

Table II. Temperature Dependences of the Pmr Parameters for 1

Temp“ VAb -7abc 6abc

71 .7 82.321 (0.004)“ 68.796 (0.004)“ 6.623 (0.004)“ 13. 525 51. 3 82.056 (0.007) 68.605 (0.007) 6.662 (0.007) 13 .451 30. 8 81.717 (0.010) 68.381 (0.009) 6.716 (0.009) 13 336 19 7 81.563 (0.007) 68.258 (0.006) 6.739 (0.006) 13 .305

-4. 3 81.180 (0.015) 67.994 (0.013) 6.760 (0.013) 13 .186 -20. 5 80.933 (0.004) 67.792 (0.004) 6.779 (0.004) 13. 141 -41 .6 80.593 (0.019) 67.575 (0.019) 6.792 (0.017) 13 .018 -61 .7 80.227 (0.005) 67.283 (0.005) 6.855 (0.005) 12 .944 -80 .6 79.866 (0.010) 67.029 (0.010) 6.912 (0.009) 12. 837 -91 2 79.703 (0.015) 66.900 (0.015) 6.923 (0.013) 12. 803

“In °C; accurate to ±1°. 6 Downfield from HMDS in Hz. c In Hz. d Values in parentheses are standard deviations.

Experimental Section 2-Methylbutane-+ was prepared in three steps according to

Scheme I.

(24) J. H. Chen and A. A. Petrauskas, J. Chem. Phys., 30, 304 (1959).

(25) E. Wyn-Jones and R. A. Pethrick, Top. Stereochem., 5, 240 (1970).

Journal of the American Chemical Society j 95:19 / September 19, 1973

6379

Scheme I

CD3MgI-Et20

Cl Cl

OH CD:i

A CD3 CD,

4 5

jTsCl/Py

CD, OTs CD,

aX LiAlH4-THF /

CD;, CD, CD; CD.

2-Methyl-3-butanoW9 (5). 2-Methyl-3-butanol-rfs (5) was pre- pared using a procedure similar to that reported by Huston, Jack- son, and Spero26 for the undeuterated compound. The apparatus, which consisted of a 500-ml three-necked flask fitted with a Hof- mann condenser, dropping funnel, nitrogen intake, and drying tubes, was dried in an oven for several hours, and flushed with dry nitrogen after assembly. Reagent grade magnesium turnings, 5.20 g (0.214 mol), and a small quantity of methyl-rf3 iodide (Stohler, 99.5% D) were added. The mixture was stirred vigorously and the remaining methyl-^ iodide (30 g total or 0.211 mol), dissolved in 100 ml of anhydrous ether, was added dropwise over a 1.5-hr period. Following the addition, the mixture was stirred for an additional 0.5 hr. Chloroacetyl chloride, 5.96 g (0.0527 mol), was dissolved in 100 ml of anhydrous ether, and added dropwise to the Grignard over a 1-hr interval so as to maintain a mild reflux. The ether was removed by distillation and the residue heated for 2 days at 95-100°.

The tarry residue was hydrolyzed by addition of ice, 100 ml of ether, and concentrated hydrochloric acid until the mixture was just acidic. The aqueous phase was extracted ten times with about 300 ml of ether, and the ether was dried over anhydrous potassium carbonate and sodium sulfate, and filtered. The filtrate was dis- tilled slowly through a vacuum-jacketed Vigreux column. Several fractions were collected and analyzed by glc. The final two frac- tions (2.80 g, 55% theory), bp 94-112° (lit. bp 112° (734 mm)), were suitable for the next reaction. The undecoupled nmr spectrum of

(26) R. C. Huston, R. I. Jackson, and G. B. Spero, J. Amer. Chem. Soc., 63, 1459 (1941).

5 exhibits three broad signals at 1.6 (C-H ß to OH), 2.1 (C-H a to OH), and 3.5 (OH), with the expected integration ratio 1:1:1.

Methyl-3-butanol-c/g Tosylate (6). To a stirred solution of 2.35 g (0.0242 mol) of 5 in 20 ml of dry reagent grade pyridine which was cooled in an ice bath was added dropwise a solution of 9.25 g (0.0484 mol) of p-toluenesulfonyl chloride in 20 ml of pyridine. Pyridinium chloride crystallized out after about 15 min. The reac- tion mixture was sealed in a flask and left for 2 days at 7°. After this time, the mixture was poured over ice and concentrated hydro- chloric acid added until the resultant mixture was distinctly acid. The product was extracted three times with ether, and the combined ether extracts were washed with 5% hydrochloric acid and water and then dried over a mixture of anhydrous potassium carbonate and sodium sulfate. After filtration, the ether was removed on a rotary evaporator, and the residue was dissolved in pentane. The pentane was distilled and the process was repeated until no water droplets were observed in the distillate. The dry tosylate (6) was recrystallized three times from pentane, yield 5.36 g (88.5%), mp 20—21 °. The undecoupled nmr spectrum of 6 exhibits an AB quartet centered at 7.6 (aromatic), a broad doublet at 4.5 (H a to -OTs), a singlet at 2.4 (aromatic methyl), and a múltiple! at 1.8 ( ß to -OTs), with the expected integration ratio 4:1; 3:1.

2-Methylbutane-ífg (1). Reagent grade tetrahydrofuran (30 ml) was distilled from lithium aluminum hydride into a dry three- necked 100-ml flask. The flask was fitted with a condenser and a pressure-equalizing dropping funnel with an intake for dry nitro- gen. Lithium aluminum hydride, 2.0 g (0.052 mol), was added slowly through a powder funnel. The stirred mixture was heated in an oil bath at 65-70°, and 3.0 g (0.012 mol) of three times re- crystallized 5 dissolved in 20 ml of dried tetrahydrofuran was added dropwise. The vaporized hydrocarbon, 1, was conducted through a micro purification train connected to the generating apparatus, consisting of bromine water (to remove 2-methyl-2-butene which was previously detected by glpc), sodium thiosulfate solution, and two ethylene glycol bubblers (to remove tetrahydrofuran solvent), and a tube of Drierite. Purified 1 was conducted finally through a finely drawn polyethylene tube into a constricted nmr tube im- mersed in a Dry Ice-2-propanol bath. A previous undeuterated sample, prepared and purified in the same way, was found by glpc to be pure.

Acknowledgment. The authors are grateful to the National Science Foundation for Grant No. GP-3815 which provided support for this work.

Stereochemical Control of Reductions. III. An Approach to Group Haptophilicities1

Hugh W. Thompson* and Richard E. Naipawer2

Contribution from the Department of Chemistry, Rutgers University, Newark, New Jersey 07102. Received January 15, 1973

Abstract: The tetrahydrofluorene system 1, angularly substituted with a series of functional groups R, has been catalytically hydrogenated over a palladium catalyst. For each functional group the percentage of cis isomer in the product is taken as a measure of that group’s tendency, termed haptophilicity, to be bound to the catalyst sur- face during olefin reduction and thereby to enforce addition of hydrogen from its own side of the molecule. The nature of haptophilic activity and its correlation with various measures of group electronic characteristics and size are discussed.

Since the work of Linstead on the reduction of phen-

anthrenes,3 many of the stereochemical aspects of heterogeneous catalytic hydrogenation have been

(1) (a) Abstracted in part from the Ph.D. Thesis of R. E. N. (b) Part II: H. W. Thompson and R. E. Naipawer, J. Org. Chem., 37, 1307 (1972).

(2) NASA Predoctoral Trainee, 1966-1967. (3) R. P. Linstead, W. E. Doering, S. B. Davis, P. Levene, and R. R.

Whetstone, J, Amer. Chem. Soc., 64, 1985 (1942), and following articles.

made comprehensible in terms of the approach, fit, and binding of the reducible molecule to the surface of the catalyst.4 These concepts have been applied with particular success to molecules whose geometry or substituents present severe steric hindrance to this

(4) (a) R. L. Burwell, Jr„ Chem. Rev., 57, 895 (1957); (b) S. Siegel, Advan. Catal. Relat. Subj., 16, 123 (1966).

Thompson, Naipawer / An Approach to Group Haptophilicities

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